1. Field Of The Invention
This invention is related to producing oxygen and to producing oxygen from lunar or martian materials; in one aspect to producing oxygen on the moon; and in another aspect to such a process in which oxygen is produced from lunar ilmenite in which sulfuric acid is recycled and titanium dioxide and iron are produced as by-products.
2. Description Of Related Art
There are many methods for producing oxygen from oxygen bearing minerals, a few of which use the mineral ilmenite as the feedstock. These tend to use extremes of temperature or of other processing parameters. One of the most common processes, the hydrogen reduction of ilmenite, is done at a relatively high temperature and results in high power consumption.
While the prior art teaches how to carry out many of the individual steps disclosed in this invention, many prior art processes are not concerned with producing oxygen and do not provide any motivation to make the combination claimed herein.
One existing commercial process, the "sulfate process", for producing titanium dioxide (TiO.sub.2) from ilmenite utilizes sulfuric acid. The ilmenite is digested with concentrated acid to produce a porous cake consisting of ferrous and titanium sulfates. This mixture is dissolved in water, cooled to crystallize out and filter FeSO.sub.4 .multidot.7H.sub.2 O, and then heated to convert the hydrolytically unstable TiOSO.sub.4 to TiO.sub.2. For this process to occur rapidly, there is a limit on the amount of excess sulfuric acid. Practically, this requires a high concentration of sulfuric acid in the digestion step. Since TiO.sub.2 product is to be used as a white pigment, efforts are made to prevent any colored ferric ion from forming. The calcining of the final TiO.sub.2 is done at 900-950 degrees Centigrade under controlled conditions (and at one atmosphere pressure) since its crystalline form is important.
In another existing process, "electrolytic iron" is produced by reduction of FeSO.sub.4 .multidot.7H.sub.2 O. This material is also used quite often in electroplating of objects with iron at the cathode. Oxygen is released and allowed to escape at the anode.
Sulfuric acid has been a commodity chemical for decades. Perennially, it is the largest volume chemical produced in the world. The economy of most major countries can be judged by its sulfuric acid consumption. There is an enormous amount of knowledge in the prior art on its manufacture, recovery, purification, and handling.
U.S. Pat. No. 3,773,913 discloses a process directed specifically to the production of oxygen on the moon using lunar materials. Lunar soil, known as regolith, is collected and separated. Ilmenite is then separated out as the material of choice. An electrolysis step is then performed. Fluorine is used as the first chemical reaction step, producing a variety of metal fluorides and releasing oxygen gas directly. This process is based on standard geochemical analytical chemistry in which fluorine or hydrofluoric acid is used to completely digest the sample. Potassium vapor and an electrolysis recovery step that do not release oxygen are involved.
U.S. Pat. No. 3,888,750 discloses that there are two basic methods used in the production of oxygen. The first is the separation of water into its constituent components. The second is the use of a membrane to separate oxygen from other atmospheric gases. This should be expected for earthly uses, since water is abundant and easily converted. This process is aimed at the production of hydrogen, which is released during an electrolysis of sulfurous acid, not sulfuric acid. No oxygen is released in this step. Sulfuric acid is made due to the oxidation of the sulfurous acid, which is then taken to a separate, thermochemical step to release oxygen by high temperature decomposition.
U.S. Pat. No. 4,053,573 discloses the recovery and reuse of the sulfuric acid in an energy efficient manner. A heating and cooling cycle is introduced which varies in temperature from 160.degree. C.-250.degree. C. The lower operating temperatures account for the energy savings.
U.S. Pat. No. 4,082,832 discloses a process for the recovery of sulfuric acid, H.sub.2 SO.sub.4, in the production of titanium dioxide, TiO.sub.2, from the raw material ilmenite. This patent describes the reduction of energy consumed in the concentration process of the acid recovery by pretreating the waste acid. FeSO.sub.4 .multidot.nH.sub.2 O, (a by-product of the pretreatment process) is dissolved in water or acids. The process is repeated several times increasing the sulfuric acid content on each successive cycle. The energy input is low for this procedure. This process is an improvement upon the existing sulfate route to titanium dioxide aimed at recycling sulfuric acid and recovering trace metals. This process isolates ferrous sulfate which then undergoes a series of oxidations (with Cl.sub.2 gas or air) and reductions, resulting in iron oxides or hydroxides as the final product. Oxygen production is not an object of this process.
U.S. Pat. No. 4,440,734 discloses a process for the recovery of sulfuric acid which requires significantly less energy than conventional processes. It is directed to the TiO.sub.2 pigment production industry. A liquid/liquid process is employed to separate the vanadium, iron, titanium, aluminum and chromium impurities from the dilute sulfuric acid. This is accomplished at room temperature as compared with the known prior art high temperature decomposition process (1,000.degree. C.). In the disclosed process spent sulfuric acid is recovered via a liquid/liquid extraction technique.
U.S. Pat. No. 4,663,131 discloses TiO.sub.2 production by using H.sub.2 SO.sub.4 to digest Ti containing material to form a cake that is easily soluble. Ilmenite is used as the raw material. An object of the invention concerns the recovery of H.sub.2 SO.sub.4 and another is the modification of the process allowing the use of H.sub.2 SO.sub.4 at a much lower concentration (75%). This process improvement to the existing sulfate route to titanium dioxide aims at reducing the volume of waste sulfate and sulfuric acid streams, thus reducing pollution. It also lowers the cost of the existing process due to this improvement and the ability to recycle some of the intermediate. The process is not concerned with producing oxygen by the electrolysis of the ferrous sulfate made as a by-product. By-product ferrous sulfate is used to lower the strength of the sulfuric acid required for use in the batch process.
U.S. Pat. No. 4,997,533 specifies hydrochloric acid as the medium for carrying out its process to produce oxygen. Chlorine can be and is released upon electrolysis of the chloride solution.
There has long been a need for an efficient and effective process for producing oxygen in outer space, e.g. from lunar materials on the moon. There has long been a need for such a process which can be practiced on the moon. There has long been a need for such a process whose power requirements can be met in a lunar environment.